n + d = 30

5n + 10d = 200  (cents)



Substituting for n:

5(30-d) + 10d = 200

150-5d + 10d = 200

5d = 50

d=10 ==>  n=20



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Ans: Sonja has 10 dimes and 20 nickels

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Check: 10*10+20*5 = 100+100 = 200 (=$2.00)  (ok) 

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